THE TRANSPORTATION OF LIQUIDS 121 then flow in by gravity, as in the Wheeler system. If not the empty tank may be connected to the suction side of the air compressor and a partial vacuum produced, as in the Harris system. The acid egg is of particular advantage in chemical establishments for the cheap intermittent handling of highly corrosive fluids.1 The Starrett air lift pump described in Eng. and Min. Journ., Mar. 30, 1907, utilizes two displacement chambers from which the air alternately displaces the water by pressure, after which the same air is allowed to escape up the stand pipe and, in the manner of the air lift, assists in raising the water and increasing the effective head. A test of such a pump by H. C. o.i FIG. 15.—Arrangements of air lifts. Behr (Cal Min. Bur., Bull 9) gave an efficiency of 50 per cent at the compressor, and 35 per cent net. The air lift consists of a drop pipe placed in a well with its lower end submerged, so that it is under the free pressure of the water more or less filling the well. An air pipe delivers air at the bottom of the drop pipe and forms a mixture of air and water which is lighter TABLE S.-ECONOMICAL CAPACITY AND than the column rf goM water DIMENSIONS OF AIB LIFTS WITH ^ h wd] c uentl the CENTRAL AIR PIPE . , . . ^. , , - mixture rises above the level of the surrounding water. The displacement of the air compressor required per gallon of water pumped is D = kl /585 log [1 + (s/34)] cu. ft., where I = lift in feet, measured from the lower water level, when pumping, to the point of discharge, s = submergence below the lower water level, feet when pumping, k — a coefficient taking care of all the losses, approximately k = 3 + (Z/700). The operating pressure = s ft. water col., is riot always known in advance, as the water will stand at a lower level when pumping than when not pumping, and it is the former that determines the point from which the submergence is measured. The central air pipe system, although obstructing the passage to some extent, has the advantage over the other systems in that the submergence can be changed con- Diameter of Gallons per Well, Drop Air based on a velocity of inches pipe, inches pipe, inches 4 ft. per second 4 3 1 70 5 3H 11A 95 6 4 11A 125 6 4K ll/2 158 7 5 2 195 8 6 2K 280 9 7 2K 380 10 8 3 500 12 10 4 780 1 This apparatus is a container of oval shape similar to Fig. 14. Such an egg-shaped vessel is free from pockets and is readily drained.